1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine and the like, which utilizes an electrophotographic process, and more particularly, it relates to an image forming apparatus wherein an image forming unit is shifted in the image forming apparatus to which an original support plate is fixed, thereby forming an image.
2. Related Background Art
In an image forming apparatus such as an electrophotographic copying machine and the like, which utilizes an electrophotographic process, a surface of an original or manuscript is exposed by an exposure device to form an electrostatic latent image on a photosensitive member as an image bearing member, the electrostatic latent image is visualized as a developed image by means of a developing device, and then the developed image is transferred onto a transfer sheet by a transferring device, and the developed image transferred to the transfer sheet is fixed by a fixing device to obtain a permanent image.
Some of such image forming apparatus are so designed that the exposure device, photosensitive member, developing device and transferring device are assembled as a integral unit, and the unit is reciprocably shifted with respect to a fixed original support plate to perform a required copying operation (for example, refer to the Japanese Patent Laid-Open No. 57-151983).
However, in such a conventional image forming apparatus, since a fixing device is fixedly attached to a body of the image forming apparatus, it is necessary to devise the timing such that the transfer sheet after the transferring operation is sent to the fixing device, and thus, this apparatus has not yet been practically used. Further, even if the unit is removable with respect to the image forming apparatus, after the unit is dismounted from the image forming apparatus, the latter cannot be used for forming the image, and, and thus, thus there arises a problem that the multi-function of the unit cannot be attained.
On the other hand, in a copying machine, it is practical that the image on the original is properly focused onto the photosensitive member by the adjustment of the height of the original support glass plate, adjustment of focus of an optical lens, or the combination thereof. Accordingly, in such copying machine, once the focusing operation has been performed, the re-adjustment of the focus is not needed, so long as there is no trouble as varying the setting in use.
However, if it is assumed that the unit by which the image forming can be effected within the image forming apparatus as mentioned above and by which the image forming can also be effected outside the image forming apparatus is used, when the exchanged unit is used within the image forming apparatus and when the unit is used outside the image forming apparatus, it is necessary to adjust the focus of the optical system, respectively, and, thus, there arises a problem that the handling of the apparatus and unit becomes complicated and troublesome. In particular, when the unit dismounted from the image forming apparatus is used together with other option apparatus, an operator is subject to considerable burden.